1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, and a computer program product.
2. Description of the Related Art
The technologies of an indirect transfer method and a direct transfer method are known as mechanisms for performing both black-and-white printing and full-color printing in an electrophotographic system. In the indirect transfer method, if black-and-white printing is performed, a black image is temporarily transferred onto an intermediate transfer unit and then the black image transferred onto the intermediate transfer unit is transferred onto a sheet. If full-color printing is performed, a full color image, which is formed by superimposing images in different colors, is transferred onto an intermediate transfer unit and then the full-color image transferred onto the intermediate transfer unit is transferred onto a sheet. In the direct transfer method, if black-and-white printing is performed, a black image is directly transferred onto a sheet. If full-color printing is performed, an image in each color is directly transferred onto a sheet.
If color matching (alignment) among images in different colors that are transferred onto a sheet by an indirect transfer method is performed, the images in the different colors are temporarily transferred onto an intermediate transfer unit and alignment control is performed by reading the images in the different colors that are transferred onto the intermediate transfer unit. On the other hand, it is generally known that, if color matching (alignment) among images that are transferred onto a sheet by a direct transfer method is performed, the images are transferred onto a sheet and alignment control is performed by reading the images transferred onto the sheet.
The alignment controls in the indirect transfer method and the direct transfer method are performed by feedback control in which the images transferred onto the intermediate transfer unit or the sheet are read; therefore, there is a problem in that, if the alignment control is performed in an image forming apparatus (see Japanese Patent Application Laid-open No. 2005-215459) that uses two transfer methods, i.e., an indirect transfer method and a direct transfer method, in combination, it is complicated and difficult to perform alignment between an image formed by the indirect transfer method and an image formed by the direct transfer method because the transfer targets are different in the indirect transfer method and the direct transfer method.